Many heat exchangers are of an indirect type which employs tubes for carrying a heat transfer fluid. A large number of tubes are mounted to extend in a parallel array between two supporting tube sheets in the heat exchanger. The tubes are pressed fit into or expanded into engagement with openings through the tube sheets, thus forming a fluid tight seal. A heat transfer fluid, such as water, is circulated through the parallel tubes between the tube sheets while a higher temperature fluid, such as combustion gases or heated water, is circulated past the exterior of the tubes between the two tube sheets for achieving an indirect heat transfer between the two fluids.
It is sometimes necessary to remove tubes from the tube sheet in which they are mounted. Removal may be necessary for many reasons, such as leaks in the tube or excessive scale accumulations within the tubes. The removal and replacement of tubes may be done on a regular preventative maintenance schedule. In any case, the replacement operation entails costly downtime for the heat exchanger. This is particularly true in the case of large electric power generating equipment where a given installation may have thousands of tubes and downtime is costly to the owner and can be inconvenient to the power customer.
To remove tubes from such a heat exchanger, the interference fit between the tube end and the tube sheet is first relieved, then the tube is axially moved several centimeters to present an end projecting beyond the tube sheet which may be gripped by a tube extractor. Typical of tube pulling devices is that shown in commonly-owned U.S. Pat. No. 3,835,520 or in U.S. Pat. No. 3,628,246.
Once the tube has been broken loose and axially moved to expose an end beyond the face of the tube sheet, it is gripped by another device of the type shown herein which rapidly moves it out of the tube sheets. Inasmuch as some tubes in such large power installations may be 10-20 meters long, the rapid removal by an extractor device is necessary to effect good economics during serving. Prior art devices for removing long tubes from tube sheets axially at high rates of speed are disclosed in U.S. Pat. Nos. 3,149,021 (Curfman) 3,785,026 (Ohmstede), and 4,044,444 (Harris) the latter being commonly owned by applicant. These devices generally comprise at least a pair of rotating rollers or drivers mounted on parallel axes and adapted for engaging in the nip a tube extending between the drivers. The drivers are rotated in opposite direction to impart an axial motion to the tube.
To provide the most efficient gripping forces between the drivers and the tubes, it is preferable that the drivers rotate synchronously, without the possibility of relative slippage between them. The apparatuses disclosed by Harris and Curfman et al. assure this desired synchronization by gearing the drivers together for operation by a single motor. However, the necessary spur gears and means for mounting them add considerable weight and expense to the extractor, increasing the difficulty of the extraction process.
Moreover, the use of spur gears to assure synchronous rotation of the drivers, as disclosed by Harris and Curfman et al., requires that the shafts mounting the gears and drivers be at a fixed distance to each other, to assure proper intermeshing of the gears. This requirement renders it difficult to adapt the extractor to accommodate tubes of different diameters.
As disclosed by Harris and Ohmstede, it has been found advantageous to grip tubes between drivers with a force sufficient to deform the tubes as they are drawn out of the tube sheet. However, scale accumulations within a tube may be sufficient to form a plug that interferes with the deformation of the tube by the drivers. Such a plug will jam an extractor having drivers mounted on fixed shafts, thus slowing the renewal process and sometimes injuring the extractor itself.
Accordingly, it is an object of this invention to provide a high speed tube remover capable of use within various sized tubes, which is jam-free, and which overcomes other deficiencies of the prior art.